We combine Galileo Solid State Imager (SSI) and Near-Infrared Mapping Spectrometer (NIMS) data to investigate the composition of pull-apart bands in Europa's Argadnel Regio. Using spectral linear mixture modeling employing cryogenic laboratory reference spectra, we find that bands of intermediate age (“grey” bands) are compositionally distinct from bands that are stratigraphically younger (“dark” bands). The grey bands have higher abundances of larger ice grains and lower abundances of hydrated salts than the dark bands; both of these tendencies are statistically significant at the 1% level. The grey and dark bands have similar abundances of hexahydrite, a material which is relatively stable under irradiation; however, the derived abundances of frozen magnesium sulfate brine and of mirabilite, which are more susceptible to fragmentation by radiation, are significantly higher in the dark bands than in the grey bands. These results are consistent with a physical model in which the differences in composition and in ice grain sizes are linked to space weathering and radiolytic processing levels; the grey bands have presumably undergone higher levels of processing, due to being exposed on Europa's surface for a longer period of time. One prominent wedge-shaped band exhibits an anomalous albedo variation across its northern portion, appearing dark in its top third, and grey in its southernmost two-thirds. We find that the dark part of the band has a modeled composition that is in-family with other dark bands, while the grey portion has a modeled composition that is indistinguishable from other grey bands in the study area. Because these variations cannot easily be attributed to the band's formation mechanism (bands open sequentially along a central axis), we surmise that the northern part has been resurfaced, probably in response to the formation of a large topographic basin that cuts through the band. Faulting accompanying basin formation may provide conduits allowing transport to the surface of materials from Europa's interior. We hypothesize that the formation of the basin resulted in fresh cryovolcanic material being deposited across the northern portion of the band, effectively “resetting” its surface age. If, as has been suggested, the giant arcuate basins resulted from an episode of true polar wander, our study may help to more tightly constrain the age of that event within Europa's geologic column.

A year and a half after its historic flyby of dwarf planet Pluto, NASA’s New Horizons spacecraft is preparing for its encounter with a second Kuiper Belt Object. Now just two years away from the planned 1 January 2019 encounter with 2014 MU69, New Horizons is in a healthy state as it sails toward the small, rocky, classical Kuiper Belt Object.

In 1976, the Viking landers carried out the most comprehensive search for organics and microbial life in the martian regolith. Their results indicate that Mars' surface is lifeless and, surprisingly, depleted in organics at part-per-billion levels. Several biology experiments on the Viking landers gave controversial results that have since been explained by the presence of oxidizing agents on the surface of Mars. These oxidants may degrade abiotic or biological organics, resulting in their nondetection in the regolith. As several exploration missions currently focus on the detection of organics on Mars (or will do so in the near future), knowledge of the oxidative state of the surface is fundamental. It will allow for determination of the capability of organics to survive on a geological timescale, the most favorable places to seek them, and the best methods to process the samples collected at the surface. With this aim, we review the main oxidants assumed to be present on Mars, their possible formation pathways, and those laboratory studies in which their reactivity with organics under Mars-like conditions has been evaluated. Among the oxidants assumed to be present on Mars, only four have been detected so far: perchlorate ions (ClO4−) in salts, hydrogen peroxide (H2O2) in the atmosphere, and clays and metal oxides composing surface minerals. Clays have been suggested as catalysts for the oxidation of organics but are treated as oxidants in the following to keep the structure of this article straightforward. This work provides an insight into the oxidizing potential of the surface of Mars and an estimate of the stability of organic matter in an oxidizing environment.

NASA took another big step to ensure reliable crew transportation to the International Space Station into the next decade. The agency’s Commercial Crew Program has awarded an additional four crew rotation missions each to commercial partners, Boeing and SpaceX, to carry astronauts to and from the International Space Station.

The four additional missions will fly following NASA certification. They fall under the current Commercial Crew Transportation Capability contracts, and bring the total number of missions awarded to each provider to six.

The additional flights will allow the commercial partners to plan for all aspects of these missions while fulfilling space station transportation needs. The awards do not include payments at this time.

“Awarding these missions now will provide greater stability for the future space station crew rotation schedule, as well as reduce schedule and financial uncertainty for our providers,” said Phil McAlister, director, NASA’s Commercial Spaceflight Development Division. “The ability to turn on missions as needed to meet the needs of the space station program is an important aspect of the Commercial Crew Program.”

The two commercial spacecraft also will provide a lifeboat capability to allow the astronauts aboard the station to return safely to Earth in an emergency, if necessary.

The ancient inhabitants of New Mexico's Chaco Canyon, the zenith of Pueblo culture in the Southwest a thousand years ago, likely had to import corn to feed the multitudes residing there, says a new University of Colorado Boulder study.

CU Boulder scientist Larry Benson said the new study shows that Chaco Canyon - believed by some archeologists to have been populated by several thousand people around A.D. 1100 and to have held political sway over an area twice the size of Ohio - had soils that were too salty for the effective growth of corn and beans.

"The important thing about this study is that it demonstrates you can't grow great quantities of corn in the Chaco valley floor," said Benson, an adjunct curator of anthropology at the University of Colorado Museum of Natural History. "And you couldn't grow sufficient corn in the side canyon tributaries of Chaco that would have been necessary to feed several thousand people.

"Either there were very few people living in Chaco Canyon, or corn was imported there."

A remarkably long period of Northern Hemispheric cooling in the 6th century CE, which disrupted human societies across large parts of the globe, has been attributed to volcanic forcing of climate. A major tropical eruption in 540 CE is thought to have played a key role, but there is no consensus about the source volcano to date. Here, we present evidence for El Chichón in southern Mexico as the most likely candidate, based on a refined reconstruction of the volcano’s eruption history. A new chronological framework, derived from distal tephra deposits and the world’s largest Holocene beach ridge plain along the Gulf of Mexico, enabled us to positively link a major explosive event to a prominent volcanic sulfur spike in bipolar ice core records, dated at 540 CE. We speculate that voluminous tephra fall from the eruption had a severe environmental impact on Maya societies, leading to temporary cultural decline, site abandonment, and migration within the core area of Maya civilization.

Although the Amazon rainforest houses much of Earth’s biodiversity and plays a major role in the global carbon budget, estimates of tree biodiversity originate from fewer than 1,000 forest inventory plots, and estimates of carbon dynamics are derived from fewer than 200 recensus plots. It is well documented that the pre-European inhabitants of Amazonia actively transformed and modified the forest in many regions before their population collapse around 1491 AD; however, the impacts of these ancient disturbances remain entirely unaccounted for in the many highly influential studies using Amazonian forest plots. Here we examine whether Amazonian forest inventory plot locations are spatially biased toward areas with high probability of ancient human impacts. Our analyses reveal that forest inventory plots, and especially forest recensus plots, in all regions of Amazonia are located disproportionately near archaeological evidence and in areas likely to have ancient human impacts. Furthermore, regions of the Amazon that are relatively oversampled with inventory plots also contain the highest values of predicted ancient human impacts. Given the long lifespan of Amazonian trees, many forest inventory and recensus sites may still be recovering from past disturbances, potentially skewing our interpretations of forest dynamics and our understanding of how these forests are responding to global change. Empirical data on the human history of forest inventory sites are crucial for determining how past disturbances affect modern patterns of forest composition and carbon flux in Amazonian forests.

Sparassodontans are a diverse but now extinct group of metatherians that were apex predators in South America during most of the Cenozoic. Studying their decline has been controversial mainly due to the scarcity of the fossil record, and different methodological approaches have led to contradictory hypotheses. In an effort to explore questions about their extinction, we developed a novel multi-model statistical approach to analyse all of the currently available data at a continental scale. Using multiple regression analysis and new advances in beta diversity analysis, we used all currently available fossil data at a continental scale to test four competing hypotheses to account for the decline of sparassodontans: competition with placental carnivorans, competition with avian phorusrhacids, non-competitive ecological interactions, and environmental fluctuations. Our results show that the sparassodontan extinction was a gradual process with species disappearing throughout the Cenozoic. Multiple regression analysis supported non-competitive ecological interactions as the best extinction model. Native South American ungulates, African migrants (caviomorph rodents and platyrrhine primates) and didelphimorphians were the groups with the highest statistical significance. Sparassodontan beta diversity increased between South American Land Mammal Ages after the Paleocene–Eocene boundary. Our results demonstrate that ecological modelling techniques illuminate aspects of extinction processes whilst mitigating the limitations of the fossil record. Our study suggests that non-competitive ecological interactions could have been the main driver for sparassodontan extinction rather than, as commonly assumed, a result of competition and/or abiotic fluctuations.

Many mammals and birds are remarkable athletes; mice work hard to dig burrows for protection and sparrows fight gravity with each flap of their wings. In order to have the energy to sustain vigorous exercise, the body's tissues need a steady supply of oxygen, and red blood cells (RBCs) are the center of the oxygen delivery system. Size matters, too; athletic mammals and birds have much smaller RBCs than other vertebrates with lesser capacities for exercise. Biologists have long been puzzled over the evolutionary origins of RBC size. Were predecessors of mammals and birds -- including dinosaurs -- athletes and did they have tiny red blood cells? How do you measure the blood of extinct animals?

Now, biologists at the University of Utah and the Natural History Museum of Utah have established a 'fossilizable' indicator of athleticism in the bones of extinct vertebrates.

The study, which published online in Current Biology on Dec. 22, is the first to draw a link between RBC size and the microscopic traces of blood vessels and bone cells inside the bone. The researchers measured the bony channels that deliver oxygen to bone tissue to pinpoint when our mammal ancestors, bird and dinosaur predecessors evolved small RBCs. They found that extinct mammal relatives, or cynodonts, and extinct bird relatives had smaller RBCs and were likely better athletes than earlier terrestrial vertebrates. The timing of RBC-size reduction coincided with the greatest mass extinction event on Earth 252 million years ago, an event that paved the way for the age of the dinosaurs.

The Shuram excursion (SE), one of the largest-known negative carbon isotope anomalies, has been globally observed in Ediacaran rocks. Precisely determining the duration of the SE is pivotal to understanding its controversial origin. Here, we present a detailed paleomagnetic, rock magnetic, cyclostratigraphic and carbon isotopic study of the SE in the Doushantuo Formation at the Dongdahe section in eastern Yunnan Province, South China. Although paleomagnetic results likely show a late Mesozoic remagnetization, careful mineralogic analyses indicate that the rock magnetic cyclostratigraphy carried by detrital pseudo-single domain (SD) or small multidomain (MD) titanomagnetite grains faithfully records orbitally-forced climate cycles in the Ediacaran. Multi-taper method (MTM) spectral analysis of magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) series reveals significant spectral peaks at similar frequencies. Based on the ratios of their frequencies, these spectral peaks are assigned to a suite of Milankovitch cycles (long eccentricity, short eccentricity, obliquity and precession), yielding a sediment accumulation rate of 1.0 cm/kyr for the Doushantuo Formation. A 9.1 ± 1.0 Myr duration is indicated for the entire SE in South China. This result is in good agreement with independent estimates from North America and South Australia, thus supporting a primary origin for the SE. In combination with published geochronologic data, we suggest that the onset of the SE occurred at ca. 560 Ma, which provides a chronostratigraphic framework for evaluating the relationship between the SE and the evolution of metazoans in Ediacaran time.

Puerto Rico's new governor was sworn in Monday, promising an immediate push for statehood in a territory facing a deep economic crisis.

Gov. Ricardo Rossello, 37, proposed several measures aimed at alleviating the crisis shortly after he was sworn in at midnight. Among them is a proposal to hold a referendum that would ask voters whether they prefer statehood or independence. Many have argued that Puerto Rico's political status has contributed to its decade-long crisis that has prompted more than 200,000 people to flee to the U.S. mainland in recent years.

"The United States cannot pretend to be a model of democracy for the world while it discriminates against 3.5 million of its citizens in Puerto Rico, depriving them of their right to political, social and economic equality under the U.S. flag," Rossello said in his inaugural speech, delivered in Spanish. "There is no way to overcome Puerto Rico's crisis given its colonial condition."

The crowd rose to its feet and cheered as Rossello announced that he would fly to Washington, D.C., Monday to back a bill to admit Puerto Rico as the 51st state.

He also said he would soon hold elections to choose two senators and five representatives to Congress and send them to Washington to demand statehood, a strategy used by Tennessee to join the union in the 18th century. The U.S. government has final say on whether Puerto Rico can become a state.

China’s mid-December abduction of a US Navy unmanned underwater vehicle (UUV) as the vessel was returning to its mothership after a scientific excursion showed that China is willing to play hardball with US hardware. In previous confrontations, China took custody of an EP-3 reconnaissance plane and its crew in 2001, and has harassed multiple unarmed US Navy survey ships with dangerous maneuvers. As part of its “peaceful rise”, China has focused on gaining ground in new domains of strategic interest outside of its traditional focus. As a result, it has adopted assertive and asymmetric strategic postures in the maritime, cyber, and space domains.

Lessons that China learns in one domain tend to find their way into others. In June 2016, China launched Aolong-1, the first of a planned series of satellites equipped with a robotic manipulator, purportedly for the purpose of capturing and de-orbiting space debris. The People’s Liberation Army (PLA) Navy destroyer that picked up the UUV in the South China Sea is tasked with and equipped for submarine recovery operations, a similarly benign mission with apparent dual-use utility. Being robotic, the UUV made for an easier, less risky, target. China learned quickly after the EP-3 incident that holding US personnel hostage for however long a period had a highly escalatory effect and was a public relations liability. A drone, though, is simply hardware, sending the desired message to the United States—and to South China Sea claimant nations—without the wetware liability.

China demonstrating its willingness to assert itself in contested domains, using tools it has developed for peaceful uses, means its assets in orbit must receive renewed scrutiny. China’s predominant doctrine for space remains a theory of “space deterrence,” its aim to hold an adversary’s space assets at risk for asymmetric advantage. What better way to send a deterrent message in space than by grabbing a high-value satellite for some period of time, potentially under the pretext of “safety of flight,” similar to the justification used by the PLA Navy in the South China Sea?